氮沉降对凋落叶分解前期土壤酶活性的影响

为了解凋落叶分解前期土壤酶活性对氮沉降的响应,通过室内模拟自然氮沉降(30 kg N·hm~(-2)·a~(-1)),设置无凋落叶(bare soil,BS)、马尾松凋落叶(Pinus massoniana litter,PL)、杉木凋落叶(Cunninghamia lanceolata litter,CL)及木荷凋落叶(Schima superba litter,SL)4种处理,恒温恒湿的条件下研究不同树种(马尾松、木荷、杉木)凋落叶分解率、土壤理化性质和土壤天冬酰胺酶及纤维素酶活性动态。结果表明:模拟氮沉降232 d后,杉木凋落叶分解最快,其次是木荷凋落叶,马尾松凋落叶分解最慢。随着外源氮的累积与凋落叶分解,凋落叶全氮含量增加,C∶N减小,土壤pH值下降显著。添加硝酸铵明显提高土壤氮素有效性。外源氮的持续输入能促进土壤纤维素酶活性增加,抑制土壤天冬酰胺酶的活性。凋落叶在分解前期抑制了土壤纤维素酶活性而后期起促进作用,但凋落叶分解对土壤天冬酰胺酶活性的影响无显著规律性。因此,氮循环将改变森林土壤C∶N比,从而影响森林生态系统的物质循环和能量流动。

Effects of simulated nitrogen deposition on soil enzyme activity during early stage of leaf fitter decomposition

In order to understand the response of soil enzyme to nitrogen deposition,four treatments,namely bare soil (BS),Pinus massoniana litter (PL),Cunninghamia lanceolata litter (CL) and Schima superba litter (SL) were set in simulated natural nitrogen deposition (30 kg N·hm-2·a-1),respectively in this study.The dynamic changes of litter decomposition of different plant (P.massoniana,C.lanceolata and S.superba) and activities of asparaginase and cellulase were analyzed during early stage of leaf litter decomposition with the constant temperature and soil water content.The results showed that the decomposition rate of C.lanceolata leaf litter was the highest,with the S.superba leaf litter in the medium and the lowest for P.massoniana leaf litter at the end of experiment.With the exogenous nitrogen accumulation and the leaf litter decomposition,total nitrogen content of leaf litter increased while C ∶ N ratio of leaf litter decreased.The value of soil pH decreased significantly.And The nitrogen availability increased distinctly by adding ammonium nitrate.The activity of cellulase was promoted by exogenous nitrogen input,but soil asparaginase activity was inhibited,inversely.Cellulase activity in soil was inhibited by the leaf litter decomposition at the early stage,but promoted at the medium and last of litter decomposition process.However,the effect of leaf litter decomposition on asparaginase activity have no significant regularity.Therefore,nitrogen cycle will change the soil C ∶ N ratio in forest,thus affect material circulation and energy flow of the forest ecosystem.